Microscopic architecture (III) Flashcards
The CNS is made up of two big groups of cells. These are what? And can you tell me what the function of the second group is, and name four types of them.
- neurons and glial cells.
- Glial cells, also known as neuroglia, are non-neuronal cells that provide support and protection to neurons.
- The types of glial cells found in the CNS are:
- 1) Astrocytes: provide structural and metabolic support to neurons, regulate the concentration of ions and neurotransmitters in the extracellular space, and play a role in the formation of the blood-brain barrier.
- 2) Oligodendrocytes: These cells produce myelin, (fatty sheath) around axons in the CNS.
- 3) Microglia: immune cells that act as the first line of defense against infections, injury, and disease.
- 4) Ependymal cells: These line the ventricles of the brain and the central canal of the spinal cord and play a role in the production and circulation of cerebrospinal fluid.
What is the neuropil and is it in white or grey matter?
Complex network of dendrites, glial cells and unmyelinated axons (you can still find a few myelinated axons) that make up the BULK of grey matter in the CNS. Cell bodies are embedded within the neuropil. It’s grey matter.
Do we use different stains to see grey and white matter microscopically? which, and how would the result look different?
- For grey matter, we use crezyl-violet (Nissl staining) that dyes things like Nissl bodies, which are the ribosomes and endoplasmic reticulum of neurons. The result is a more violet look.
- For white matter, we use luxol fast blue, which dyes the fatty myelin sheaths to show the fibres. It gives a super blue look.
Do you see oligodendrocytes and astrocytes in white matter or grey?
Oligodendrocytes are more abundant in th white matter, because of the myelin sheaths that they produce.
Astrocytes are more abundant in the gray matter.
But you can find both in both.
what MAIN structures are involved in creating CSF? What would you call the overall structure?
The production of cerebrospinal fluid (CSF) in the choroid plexus involves specialized cells and structures such as:
* endothelial and ependymal tight junctions,
* blood vessels,
* ependymal cells.
These structures work together to regulate the composition of the CSF and maintain the integrity of the blood-brain barrier and protecting it. The tight junctions between the cells of the choroid plexus and blood vessels restrict the movement of substances between the blood and CSF, while actively transporting certain molecules.
What is meant by astrocyte polarisation? Go into detail.
Astrocytes are huge multitaskers - they do two groups of things at two ends:
- The neuronal pole - glioneuronal unit, where they form a tripartite synapse. At this synapse, which consists of a pre-synaptic neuron, a post-synaptic neuron, and an astrocyte, the astrocyte does the following things: a) uptake, reuptake and converting of neurotransmitters & ions b) release of gliotransmitters (glutamate, ATP, adenosine, GABA etc) c) they can actually be EXCITED by neurotransmitters (calcium ion elevation). d) huge important role in promoting synaptogenesis.
- the vascular pole, gliovascular unit - blood brain barrier. The astrocytes accommodate local blood flow rate and BBB permeability to actual neuronl needs. contribute to the harmony between vessel & neuronal needs
Name the important strctures that typically surround a blood vessel at the blood brain barrier (=blood-CSF barrier=choroid plexus epithelium)?
From inside (blood vessel) to outside
1. Endothelial cells: forming the tight junctions in between- main part! Create a 1) physical 2) transport and 3) metabolic barrier
2. Basement membrane
3. Pericytes: regulate the diameter of the endothelial tube and therefore, blood flow.
4. Astrocytes: with aquaporin-4 at the astrocytic endfeet (important passive pore that lets H2O through contributing to limiting brain edema formation). Also modulate lots of functions.
5. Microglia: detecting and sealing mild BBB leakage
Give an example of things that happen to the BBB during a problem like meningitis or ischaemia?
BBB disruption –>
* endothelial tight junctions are lose, fenestration occurs.
* Astrocyte end-feet swell and detach from the surface
* basement membrane becomes thinner and less supportive
* migroglial reaction
* plasma protein leakage
What obvious things normally pass, pass with regulated transport, and do not pass through the BBB?
- Passes: O2, CO2, small lipophilic molecules,
- regulated transport: small hydrophilic molecules (nutrients
- excluded: large hydrophilic molecules (peptids)
So if small hydrophylic molecules pass through the BBB with tight regulation and large hydrophilic molecules (peptids) are excluded, how do hormones and neurohormones pass through the BBB to and from the CNS? Give examples
The Circumventricular Organs!! (CVOs)
These are structures centred around the ventricles that lack a regular BBB, they are “leaky” regions that are isolated from the rest of the brain & CSF through tancytes - specialised ependymal cells that control regulated transport.
Examples of CVOs?
* pineal body (melatonin secretion)
* neurohypophsyis (oxytocin release)
* subfornical organ (angiotensin II level monitoring)
Why is fatal familial insomnia related to the BBB?
Genetic disease - hypothesis is that the mutations may affect the ability of the BBB to prevent the entry of abnormal prion protein into the brain.
What is the glymphatic system? Is it a lymphatic system?
The glymphatic system:
A waste clearance system in the brain that is responsible for the removal of toxic waste products, such as beta-amyloid and tau proteins, from the brain. Involves the BBB and the flow of cerebrospinal fluid (CSF) through the brain’s extracellular spaces, facilitated by the expansion and contraction of astrocytes (involves aquaporin-4). This process is thought to occur primarily during sleep, when the brain’s metabolic rate decreases and allows for more efficient waste clearance.
It is not a lymphatic system, but is called “glymphatic” because it is named after its key player, the glial cells in the brain, specifically astrocytes, and its function, which is to act like the lymphatic system in the body by clearing waste products.
What is the ECM (extracellular matrix)?
What % of the brain is composed of ECM? And what are the 2 main classes of ECM macromolecules?? Which class of these macromolecules can you find more of in the brain?
What’s an example of a very important ECM in the brain?
- The extracellular matrix (ECM)
= The network of proteins and carbohydrates that surround a cell or fill the intercellular spaces.
/the non-cellular component present within all
tissues and organs, that provides not only essential physical scaffolding for the cellular constituents but also represents crucial biochemical and biomechanical
cues that are required for tissue morphogenesis, differentiation and
homeostasis. - 10-20% of total brain volume
- 2 main classes of ECM macromolecules: 1. proteoglycans and 2. fibrous proteins (e.g, collagen, fibronectin, elastin)
- In the brain, you find proteoglycans and glyproteins. Not fibrous components, except the basal membrane.
- Perineuronal nets (PNNs) - specialized extracellular matrix structures that surround certain neurons in the CNS. They are composed of glycoproteins and proteoglycans and play a crucial role in stabilizing neuronal connections and protecting neurons. PNNs are also involved in regulating synaptic plasticity, which is important for learning and memory processes, and are also involved in synaptogenesis!!
